The present invention is related to a method to quantify conjugated dienes in hydrocarbon feedstream and product. In particular, the method determines the molar concentration and/or the carbon number distribution of the conjugated dienes.
Conjugated dienes are a major class of compounds in hydrocarbon systems that are responsible for deposit formation in refinery conversion units such as hydrocracking and hydroconversion conversion units and fractionators and heat exchangers. They are also responsible for deposit formation in automobile engines. The information is critical for assessing the potential of forming deposits in a hydrocarbon system. Knowledge of the concentration and types of conjugated dienes provides guidance to the refinery on the necessity of pretreating the refinery feed, such as installing a diolefin saturator prior to processing in order to prevent fouling during processing. In fuel applications, the information may be used to determine, e.g. if and how much a naphtha can be blended into fuel or if the naphtha needs to be hydrotreated, etc.
There are no reliable established methods to identify and quantify conjugated dienes, acyclic and cyclic, in hydrocarbon systems. GC/FID can be used to quantify small conjugated dienes (Less than C6) in low boiling hydrocarbon systems. The identifications were made based on retention times and mass spectral library matches. The method cannot identify/quantify large conjugated dienes (Greater than C6) due to the low concentrations of the analytes, severe overlaps with other hydrocarbon components and very similar mass spectra between conjugated and non-conjugated dienes.
Bromination has been widely used to determine olefin content (including conjugated dienes) in hydrocarbons. It can not differentiate conjugated dienes from other olefins. Aromatics, especially phenols, can interfere with the analysis.
The MAV test is a semiquantitative method developed by UOP and uses maleic anhydride as a derivatization agent. The reaction is not selective and cannot proceed quantitatively. Therefore, only a relative number can be obtained. In addition, it cannot provide molecular identifications of different conjugated diene types required for refinery guidance.